Method for making mushroom-type hook strap and mushroom-type hook strap made thereby

ABSTRACT

A method for making a mushroom-type hook strap for mechanical fasteners is disclosed. In a first stage of the method, a hook strap on which a plurality of hook preforms each having a substantially V-shaped free end are integrally molded. Then, in a second stage of the method, the V-shaped free end of each the hook pefeorm is deformed into a polygonal head portion by two calendar rolls so as to form a mushroom-type hook strap that has a higher engaging percentage with the loop strap, has a longer lifetime, and is capable of providing a reliable and all-directional uniform fastening function.

FIELD OF THE INVENTION

The present invention relates generally to a method for making a hookstrap for mechanical fasteners, and more specifically to a method formaking a mushroom-type hook strap for mechanical fasteners and amushroom-type hook strap made thereby.

BACKGROUND OF THE INVENTION

A hook-and-loop fastener is a well know fastener type and wildly adaptedin a variety of fields that need to fasten two articles together, suchas garment, hats/caps, sporting goods, etc.. A hook-and-loop fastenermainly consists of a hook strap on which a plurality of plastic hooksare formed and a loop strap on which a plurality of fabric loops areformed and by engaging/disengaging the hooks on the hook strap and theloops on the loop strap, a fastening/unfastening function is provided.

FIG. 1 illustrates a method for making a hook strap which generallyincludes: providing thermoplastic resin 1 into a plastic extruder 2;extruding melted thermoplastic resin 1 from the extruder 2 into aplurality of die cavities 4 formed in an outer periphery of a moldingroller 3; cooling the molding roller 3 to form a hook strap 7 on which aplurality of upstanding stems 6 are molded; striping the hook strap offthe molding roller 3 by a stripping roller 5; and feeding the hook strapthrough a nip formed between a pair of shaping rollers and the shapingroller that contacts the stems heats the free end of the stems to atemperature above a flow point of the thermoplastic reason to shape thestems into hooks with desired shape.

FIGS. 2 and 3 illustrate the structure of two existing mushroom-typehook strap respectively, wherein FIG. 2 shows an array ofcircular-headed mushroom-type hooks (FIG. 2 b) that are formed fromcylindrical stems (FIG. 2 a); and FIG. 3 shows an array ofelliptic-headed mushroom-type hooks (FIG. 3 b) that are formed fromtetragon stems (FIG. 3 a). Although these two mushroom types of hooksboth may provide certain fastening/unfastening function, they both havetheir own deficiencies. For instance, when engaging the circular-headedmushroom-type hooks illustrated in FIG. 2 with the fabric loops on theloop strap, the effective engaging percentage is relative low becausethe smooth periphery of the circular head of the hooks does not provideprotruding portions that can engage with the fabric loops, and thus hasa drawback of unable to provide sufficient fastening strength.Additionally, circular-headed mushroom-type hooks can provide effectiveengaging only when the head of the hooks fully inserted into the fabricloops forming a lockup type engagement. However, although this lockuptype of engagement may provide a firm engagement, the fabric loopsusually will be destroyed by the hooks during a detaching operationbetween the hook strap and the loop strap, and after several times ofengaging/detaching operations the fastening capability will drop sharplyor even loosing the fastening capability because the percentage of theloops been destroyed increases as the engaging/detaching operationnumber increases. As a result, the effective lifetime of thiscircular-headed mushroom-type hooks is relative short.

Although the ends of the major axis of the elliptic-headed mushroom-typehooks illustrated in FIG. 3 can form effective engagement with thefabric loops and thus can provide higher engagement percentage andlarger fastening strength than above-mentioned circular-headedmushroom-type hooks, however, because this type of hooks form effectiveengagement with the fabric loops only at the ends of the major axis ofthe elliptic head, the effective fastening strength is provided only ina direction parallel the major axis of the elliptic head. The effectiveengagement with the loops in a direction perpendicular to the major axisof the elliptic head is much less than in the parallel direction. Inother words, the fastening function provided by this type ofhook-and-loop fastener is not an all-directional uniform fasteningfunction, but a directional fastening function. Therefore, when theengagement between this type of elliptic-headed mushroom-type hooks andthe loops is subjected to an external impact force in a specificdirection (such as in a direction perpendicular to the major axis of theelliptic head), an unintentional disengaging may occur and pose ainsufficient reliability problem to this type of hooks.

In view of the above-mentioned disadvantages/problems associated withthe existing mushroom-type hook strap, there exists a need for a methodfor making a mushroom-type hook strap which has a higher engagingpercentage with the loop strap, has a longer lifetime, and is capable ofproviding a reliable and all-directional uniform fastening function.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide a methodfor making a mushroom-type hook strap which has a higher engagingpercentage with the loop strap, has a longer lifetime, and is capable ofproviding a reliable and all-directional uniform fastening function.This object may be achieved by a method for making a mushroom-type hookstrap for mechanical fasteners. This method includes the steps of:

providing a rotational molding roller, the molding roller having aplurality of substantially Y-shaped molding cavities formed in an outerperiphery surface thereof and a cooling device provided therein;

providing an extruder, the extruder having a extruding die disposedimminently close to the outer periphery surface of the rotationalmolding roller with a gap being formed therebetween;

feeding a thermoplastic material to the extruder and melting thethermoplastic material in the extruder so as to extrude the meltedthermoplastic material into the plurality of substantially Y-shapedmolding cavities and onto the outer periphery surface of the rotationalmolding roller through the extruding die;

cooling the thermoplastic material on the outer periphery surface of therotational molding roller and within the substantially Y-shaped moldingcavities with the cooling device so as to form a hook strap on which anplurality of hook prefroms are molded, each preform having asubstantially V-shaped free end;

peeling off the hook strap from the molding roller; and

feeding the hook strap through a nip formed between a pair of calendarrolls, wherein the calendar roll that contacts the V-shaped free end ofthe hook preforms is heated to a temperature above a plastic deformingtemperature of the plastic material so as to deform the V-shaped freeend of each hook preform into a polygonal head shape and thereby forminga mushroom type hook having a polygonal head portion.

According to one embodiment of the present invention, the plancontaining the two intersected arms of the V-shaped free end of the hookpreform is parallel to the direction that the hook strap is fed throughthe calendar rolls.

According to another aspect of the present invention, a mushroom-typehook strap is produced by the method described above.

Features and objects of the present invention other than the above willbecome clear by reading the description of the present specificationwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic view illustrating an apparatus form makingtraditional hook straps;

FIGS. 2 a and 2 b are enlarged schematic perspective views showing thestructure of one of existing mushroom-type hooks;

FIGS. 3 a and 3 b are enlarged schematic perspective views showing thestructure of another existing mushroom-type hooks;

FIG. 4 is a schematic view illustrating an apparatus for making theinventive mushroom-type hook strap according to one embodiment of thepresent invention; and

FIG. 5 is an enlarged schematic perspective view showing the structureof the hook preforms before and after being fed through the calendarrolls.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 4 and 5 in which a preferred embodiment of themethod of the present invention and a mushroom-type hook strap madethereby is illustrated to describe the present invention.

FIG. 4 is a schematic view illustrating an apparatus 10 for making theinventive mushroom-type hook strap according to one embodiment of thepresent invention. The apparatus 10 mainly includes a rotational moldingroller 20, an extruder 30, a stripping roll 40 and a pair of calendarrollers 50 and 52. The molding roller 20 has a plurality ofsubstantially Y-shaped molding cavities 22 formed in an outer peripherysurface thereof and a cooling device (not shown), such as a coolingwater circulating system, provided therein. The extruder 30 includes amelting chamber 32 for melting the plastic material, and the meltingchamber 32 is surrounded by heating coils 33. The extruder 30 furtherincludes a feed tank 34 disposed at one end of the melting chamber 32and an extruding die 36 operationally coupled to the other end of themelting chamber 32. The extruding die 36 is disposed imminently close tothe outer periphery surface of the rotational molding roller 20 with agap being formed therebetween. This gap may be varied by moving theextruding die 36 relative to the outer periphery surface of therotational molding roller 20.

When executing the inventive method of the present invention, athermoplastic material (for example, polyethylene) is firstly suppliedto the feed tank 34 and through which the thermoplastic material is fedinto the extruder 30. The thermoplastic material is melted in themelting chamber 32 by the heating coils 33 (for example, the temperaturein the melting chamber is heated up to 235° C.). The meltedthermoplastic material is then ejected through the extruding die 36 ontothe outer periphery surface of the rotational molding roller 20 and intothe plurality of substantially Y-shaped molding cavities 22. After thethermoplastic material that on the outer periphery surface of therotational molding roller 20 and within the plurality of substantiallyY-shaped molding cavities 22 is cooled and solidified by the coolingdevice of the molding roller 20, it is peeled off from the moldingroller 20 by a stripping roll 40 to formed a hook strap 60 and the hookstrap 60 includes a backing 62 and a plurality of hook preforms 64integrally molded on the backing 62. The hook strap 60 is then fedthrough a nip formed between the calendar rolls 50 and 52.

In the embodiment shown in FIG. 5, each of the preforms 64 is moldedinto a polygonal peg (such as a tetragon peg as shown in the drawing)and includes a stem portion 66 and a substantially V-shaped free end 68.In addition, in the embodiment shown in FIG. 5, the plan that containsthe intersected arms of the V-shaped free end of the hook perform 64 isparallel to a direction D that the hook strap 60 is fed through thecalendar rolls 50 and 52.

The calendar roll 50 that contacts the V-shaped free ends of the hookpreforms 64 is heated to and maintained at a plastic deformingtemperature of the thermoplastic material. For example, in the case thatpolyethylene is used as the thermoplastic material the calendar roll 50is heated to and maintained at 130° C. Additionally, a nip is formedbetween the calendar rolls 50 and 52 and this nip can be adjusted suchthat the nip is smaller than a sum of the thickness of the backing 62and the height of the preform 64 and substantially equal to the heightof the stem portion 66 of the hook preform 64. Thereby, while being fedthrough the calendar rolls 50 and 52, the V-shaped free end 68 of thepreform 64 will be plastically deformed as a polygonal head portion 68′,as shown in FIG. 5.

Because the hooks of the hook strap produced by the method of thepresent invention has a polygonal head portion 68′, a number ofprotruding portions are provided by the head portion 68′ to formeffective engagement with the loops of a loop strap and a higherengaging percentage can thus be provided. In addition, because the hooksof the hook strap of the present invention engage the loops of a loopstrap with the protruding portions of polygonal head portion, no loopswill be destroyed during a detaching operation and thus a longerlifetime for the hook strap may be provided. Moreover, the polygonalhead portion of the hooks of the hook strap of the present inventionprovides protruding portions in substantially every direction forengaging the fabric loops of a loop strap and thus the hook strap of thepresent invention can provide a uniform engaging function insubstantially all direction.

Although the present invention has been described above according to thepreferred embodiment thereof, this does not mean that the scope of thepresent invention is limited to specific structure and operation stepsdescribed above. In fact, there exist various modifications andvariations under the principle and spirit disclosed above. For instance,an auxiliary cooling device, such as a cooling fan, may be disposedrelative to the molding roller 20 at a position diametrically oppositeto the extruding die 36 to provide extra cooling effect to the hookstrap on the outer periphery surface of the molding roller 20.

It will be apparent to people skilled in this art that manymodifications can be made to the disclosed structures/steps withoutdeparting from the scope of the invention. Therefore, it is the intentof the appended claims to cover all such variations and modifications ascome within the sprit and scope of this invention.

1. A method for making a mushroom-type hook strap for mechanicalfasteners, the method comprising the steps of: providing a rotationalmolding roller, the molding roller having a plurality of substantiallyY-shaped molding cavities formed in an outer periphery surface thereofand a cooling device provided therein, the Y-shaped molding cavitieseach having a wider bottom than a top opening on the outer peripherysurface; providing an extruder, the extruder having a extruding diedisposed imminently close to the outer periphery surface of therotational molding roller with a gap being formed therebetween; feedinga thermoplastic material to the extruder and melting the thermoplasticmaterial in the extruder to extrude the melted thermoplastic materialinto the plurality of substantially Y-shaped molding cavities and ontothe outer periphery surface of the rotational molding roller through theextruding die; cooling the thermoplastic material on the outer peripherysurface of the rotational molding roller and within the substantiallyY-shaped molding cavities with the cooling device to form a hook strapon which a plurality of Y-shaped hook prefroms are molded, each saidY-shaped preform having a substantially V-shaped free end; peeling offthe hook strap from the molding roller; and feeding the hook strapthrough a nip formed between a pair of calender rolls, wherein thecalender roll that contacts the V-shaped free end of the hook preformsis heated to a temperature above a plastic deforming temperature of thethermoplastic material to deform the V-shaped free end of each hookpreform into a polygonal head shape and thereby forming a mushroom typehook having a polygonal head portion.
 2. A method for making amushroom-type hook strap for mechanical fasteners according to claim 1,wherein a plane that contains the two intersected arms of the V-shapedfree end of the hook preform is parallel to the direction that the hookstrap is fed through the calender rolls.
 3. A method for making amushroom-type hook strap for mechanical fasteners according to claim 1,wherein the gap between the extruding die and the outer peripherysurface of the rotational molding roller can be adjusted by moving theextruding die relative to the molding roller.
 4. A method for making amushroom-type hook strap for mechanical fasteners according to claim 1,wherein the peeling off step is performed by a rotational strippingroll.
 5. A method for making a mushroom-type hook strap for mechanicalfasteners according to claim 1 further comprising the step of providingan auxiliary cooling device outside the molding roller to provide extracooling to the outer periphery surface of the rotational molding roller.6. A mushroom-type hook strap for mechanical fasteners which is producedby using a method according to claim
 1. 7. A method for making amushroom-type hook strap for mechanical fasteners according to claim 1,comprising the additional step of adjusting the nip formed between thecalendar rolls to be smaller than sum of thickness of backing and thepreforms of the strap.
 8. A method for making a mushroom-type hook strapfor mechanical fasteners according to claim 1, wherein the polygonalhead portion of each said perform is octagonal in shape.